4.2 Spectroscopic Insights into the Mechanism of N 2 Reduction
The binding of N 2 plausibly occurs via a reductive elimination mechanism. Insight
into N 2 binding was provided by Hoffman and co-workers who used freeze-quench
trapping to accumulate an intermediate species. Its presence was first noticed in an
aVal70 to aIle70 point mutant of NifDK (designated NifDK
Ile70 ) with impaired
ability to reduce all known substrates except protons, but which could later also be
identified in wild-type NifDK [88, 89]. For this intermediate, the presence of a
paramagnetic S = 1/2 EPR signal indicated that NifDK is in an even-numbered
state while kinetic analysis suggested that this intermediate is either three or four
172
C.-C. Lee et al.
The binding of N 2 plausibly occurs via a reductive elimination mechanism. Insight
into N 2 binding was provided by Hoffman and co-workers who used freeze-quench
trapping to accumulate an intermediate species. Its presence was first noticed in an
aVal70 to aIle70 point mutant of NifDK (designated NifDK
Ile70 ) with impaired
ability to reduce all known substrates except protons, but which could later also be
identified in wild-type NifDK [88, 89]. For this intermediate, the presence of a
paramagnetic S = 1/2 EPR signal indicated that NifDK is in an even-numbered
state while kinetic analysis suggested that this intermediate is either three or four
172
C.-C. Lee et al.